This invention relates to the improvement of substrate alignment, for example in the manufacture of semiconductors.
The manufacture of semiconductors requires that patterned layers be aligned to specific underlying features. The amount of misalignment is readily measurable, using commercially available instruments and procedures. It is desirable to minimize misalignment. Exposure tools, such as a stepper, typically allow measured corrections to be entered so that alignment is improved on subsequent wafers.
Stepper alignment connections are typically made by measuring the alignment and reversing the measured component offsets.
There exists a problem in that one correction can interact with another, and also the response to a correction may be some fraction of the actual programmed value.
The present invention is concerned with improving the pattern alignment, i.e., reduce the pattern misalignment by calibrating the stepper and measuring component responses. These responses are regressed and input into a response matrix. The response matrix is then used to predict the required component offsets by solving the relevant set of linear equations.
Broadly, the invention is to a method for improving alignment of a substrate on a stepper, comprising the steps of imposing predetermined corrections for each of a plurality of substrates, a set of corrections for each substrate, measuring the actual corrections which occur on each substrate, mathematically processing the actual corrections to produce a matrix and provide a plurality of equations, and resolving the equations to provide a set of input corrections to provide a correct alignment.